High efficiency single turn magnetic head



'Oct. 20, 1970 A. J. FOSTER 3,535,465

HIGH EFFICIENCY SINGLE TURN MAGNETIC HEAD Filed Nov. 24, 1967 2 Sheets-$heet l INVENTOR 7//sw 21f o o i 3 9127;

AT TORUEY Oct. 20, 1970 A. J. FOSTER HIGH EFFICIENCY SINGLE TURN MAGNETIC HEAD 2 Sheets-Sheet 2 Filed Nov. 24, 1967 M, io acaweg M761 United States Patent 3,535,466 HIGH EFFICIENCY SINGLE TURN MAGNETIC HEAD Allen J. Foster, Clementon, N.J., assignor to RCA Corporation, a corporation of Delaware Filed Nov. 24, 1967, Ser. No. 685,354 Int. Cl. Gllb /20 US. Cl. 179--100.2 7 Claims ABSTRACT OF THE DISCLOSURE There is disclosed a magnetic transducer for use in recording and reproducing apparatus. The transducer comprises a single turn of wire mounted through the gap between independent pole pieces which are separated by a non-magnetic spacer. The single turn links a high efliciency magnetic toroidal transformer which is an integral part of the transducer for providing appropriate operating signal levels. The whole assembly is mounted in and supported by a pair of clamping blocks which can be secured together by a pressure screw.

BACKGROUND OF THE INVENTION Single turn heads have been known in the art for some time but have had limited use because of severe problems of fabrication and operation. In the typical prior art heads a conductor usually consisting of metal foil forms the single turn which is mounted between the pole tips in the same place occupied by a gap spacer in a conventional ring head. However at video frequencies the gap dimensions must be kept small to insure proper frequency response. This permits only a very small cross-sectional area of the single turn which limits its current carrying capability and therefore reduces transducer efficiency. To remedy this problem attempts have been made to couple the single turn to a remote transformer. However the leads required introduce intolerable amounts of stray inductance which degrade performance especially at high frequencies. Alternatively the transformer has been brought in closer proximity by utilizing a portion of one of the magnetic legs of the head core as the core for the transformer. While this reduces the inductance, it introduces interference problems in magnetic circuits of the head.

It is therefore an object of the present invention to provide an improved single turn head capable of a high efilciency of operation.

A further object is to provide an improved single turn magnetic head in which the dimensions of the single turn are not restricted by the gap size.

Still a further object is to provide an improved magnetic head transducer having minimal lead inductance, a minimum susceptance to secondary gap effects and wherein stray field pick-up is virtually eliminated.

These and other objects are accomplished according to one embodiment of the present invention by providing a very short magnetic path thereby requiring less drive current. This path comprises the proximate portions of the juxtaposition pole pieces, a single turn disposed through the pole pieces and the portion of the recording medium adjacent to the gap formed by the pole pieces. This compactness of the magnetic circuit is due to the skin effect in the magnetically separated pole pieces at high frequencies which sets up eddy currents in the extremes of the pole pieces thereby containing the magnetic lines to the gap vicinity. The resultant efficiency of the magnetic circuit permits the use of a pole piece material which is less eflicient magnetically but more resistant to wear. The single turn also links a toroid of high efficiency magnetic material having an independent multiple turn secondary 3,535,466 Patented Oct. 20, 1970 ice winding to form a transformer which provides the required signal transfer characteristics. The mounting of the toroid in close proximity to the pole pieces but magnetically independent of them, eliminates magnetic circuit interference and reduces lead inductance. Secondary gap effect which is caused by the grain boundaries in the pole tip material is virtually eliminated by proving a hole in the pole pieces for the single turn which is small.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a view of a magnetic head according to one embodiment of this invention.

FIG. 2a-b are views of a magnetic head according to another embodiment of this invention.

FIG. 3 is an expanded view of one portion of the head of FIG. 2.

FIG. 4 is an expanded sectional view of another portion of the head of FIG. 2.

DISCUSSION OF THE DRAWINGS FIG. 1 shows a magnetic transducer comprising a pair of separate magnetic pole pieces 3 and 4 mounted in a pair of C-shaped non-magnetic clamping blocks 1 and 2. The pole pieces 3 and 4 are preferably constructed from a material such as Alefcon whose characteristics are a compromise between high magnetic efiiciency and good wear resistance. However, the pole pieces 3 and 4 may also be formed from a ferrite material. Clamping blocks 1 and 2 are preferably made of a hard non-magnetic material such as brass and contain slots 17 and 18 respectively in which are mounted pole pieces 3 and 4. Each of the pole pieces 3 and 4 contain a groove therethrough in the abutting pole faces which together form the aperture 12 having a diameter of approximately .005 inch. An insulating layer of Silicon Monoxide of approximate thickness of 50 micro inches is disposed between the abutting faces of pole pieces 3 and 4 to form the working gap 13, The surfaces 14 and 16 of the pole pieces and the plane of joinder 15 of the clamping blocks are similarly covered with a layer of Silicon Monoxide. A single closed turn 6 of electrically conductive material such as copper, silver or gold passes through aperture 12 formed at the gap 13 between pole pieces 3 and 4. The single turn 6 further couples to a toroidal core '5 of high magnetic permeability such as ferrite, which is disposed within the opening of the C-shaped clamping blocks 1 and 2. A multiple turn winding 7 of the material used for single turn 6 is also wound about toroid core 5 to provide proper signal transformation to and from the working gap 13 of the head. A channel 9 is provided in clamping block 2 through which the leads of winding 7 are coupled to terminals 11 of the recessed terminal board 10. For structural integrity and proper insulation, a potting compound 8 such as Hysol cement is provided which fills the open spaces between clamping blocks 1 and 2, the channel 9 and covers recessed terminal board 10.

If reference is made to FIG. 2a there is shown a view of a magnetic transducer according to another embodiment of the invention. The structure, material and mode of operation of this transducer are identical to that of FIG. 1 with the exception of the single turn 20*. The single turn 20 of FIG. 2a is passed about core 5 and through aperture 12 in the form of a figure eight as contrasted with the elliptical shape of the single turn 6 of FIG. 1. This figure eight configuration affords increased inductive coupling in the magnetic circuit of the transducer. FIG. 2a also shows more clearly the details of the transducer structure including pressure screw 21 which engages the threaded aperture 22 of clamping block 1 to hold the head assembly together.

FIG. 2b is an end view of the transducer of FIG. 2a

showing the disposition of the toroid '5, pole piece 3, terminal board and threaded aperture 22.

FIG. 3 is an expanded view of the working gap area of the transducer of FIG. 2 showing the structural interrelation of the pole pieces 3 and 4 with the single turn 20, toroid 5 and its multiple winding 7.

FIG. 4 is an enlarged sectional view along the section line 44 of FIG. 2a which more clearly shows how the figure eight single turn winding is disposed about toroid 5 and through the aperture 12 at the gap face of pole piece 4.

What is claimed is:

1. A magnetic transducer head comprising:

(a) a pair of independent pole pieces having abutting surfaces with a gap therebetween, each of said abutting pole piece surfaces further having a groove therethrough and across the width thereof so as to form an aperture through said pole pieces at said gap, the center axis of said aperture being parallel to the transducing gap surface formed by said pole pieces;

(b) a layer of insulating material disposed in said gap on the abutting surfaces of said pole pieces including said grooves;

(c) a pair of clamping blocks of non-magnetic material, each of said blocks having a slot therein for holding a pole piece so that an opening is formed between exposed surfaces of said pole pieces and said blocks;

(d) a toroidal core member of magnetically permeable material disposed within said opening formed by said pole pieces and said clamping blocks, said core member being substantially coplanar with said pole pieces and physically separate from said pole pieces;

(e) a single unitary closed loop electrical conductor passing about said toroidal core and through said aperture formed at said gap by said pole pieces; and (f) a coil of electrically conductive vvire wound about said toroidal core member for transforming signals to and from said head. 2. The magnetic transducer head according to claim 1 wherein:

(a) said pole pieces are composed of Alfecon material. 3. The magnetic transducer head according to claim 1 wherein:

(a) said pole pieces are composed of ferrite material. 4. The magnetic transducer head according to claim 1 wherein:

(a) said insulating means comprises a layer of silicon monoxide material.

5. The magnetic transducer head according to claim 1 wherein:

(a) said closed loop electrical conductor is in the form of an ellipse.

6. The magnetic transducer head according to claim 1 wherein:

(a) said closed loop electrical conductor is in the form of a figure eight.

7. A magnetic transducer comprising; a pair of pole pieces each having first and second portions forming an obtuse angle, each of said first portions having a groove therethrough and across the width thereof, a pair of generally C-shaped clamping blocks of non-magnetic material, each of said blocks having a slot therein for receiving the second portions of said pole pieces to maintain said first portions in abutting relation with a gap therebetween, said grooves forming an aperture through said pole pieces at said gap, the center axis of said aperture being parallel to said gap formed by said pole pieces, a layer of first insulating material disposed in said gap on the abutting surfaces of said pole pieces including said grooves, a toroidal core member of magnetically permeable material disposed within an opening formed by the edges of said pole pieces and said blocks, said core member bein gsubstantially coplanar with said pole pieces, and physically separate from said pole pieces, a single unitary closed loop electrical conductor passing about said toroidal core and through said aperture, one of said blocks having a recessed surface extending between an edge defining said opening and an exterior edge of said block, a pair of terminals mounted to said block in said recessed surface, acoil of electrically conductive wire wound about said toroidal core, the free ends of said coil extending along said recessed surface to contact respective ones of said pair of terminals, and a second insulating material filling said openings and said recessed surface.

References Cited UNITED STATES PATENTS 2,591,070 4/1952 Howell 172-1002 2,838,614 6/1958 Ashby et a1. 179-1002 2,854,525 9/1958 Quade 179l00.2 3,249,927 5/1966 Page 34674 3,378,647 4/1968 Hirota 340--174.1 3,443,040 5/1969 Suzuki et al 34674 JAMES W. MOFFITT, Primary Examiner R. S. TUPPER, Assistant Examiner 

